The in-situ delivery of therapeutic agents within the body of a patient is common in the practice of modern medicine. In-situ delivery of therapeutic agents is often implemented using medical devices that may be temporarily or permanently placed at a target site within the body. These medical devices can be maintained, as required, at their target sites for short or prolonged periods of time, in order to deliver therapeutic agents to the target site.
For example, in recent years, drug eluting coronary stents, which are commercially available from Boston Scientific Corp. (TAXUS, PROMUS), Johnson & Johnson (CYPHER) and others, have been widely used for maintaining vessel patency after balloon angioplasty. These products are based on metallic expandable stents with polymer coatings that release anti-restenotic drugs at a controlled rate and total dose.
Therapeutic agents have also been delivered to vessel walls using balloons. For example, there have been clinical trials showing that in-stent restenosis can be treated using a balloon having a sprayed coating of pure paclitaxel.
Although a paclitaxel coated balloon has been shown efficient in trials, it may not always be the most desirable treatment scheme for a variety of reasons. For example, delivery of a consistent amount of drug to the lesion site may be an issue due to drug loss during delivery to the lesion (and vessel wall) before and after balloon inflation. Moreover, the contact time between the therapeutic-agent-coated surface and the vessel wall maybe limited due to the fact that the balloon acts to block blood flow. Furthermore, dilatation of a vessel by means of some balloons may cause overstretching of tissues in the vessel wall, which can result in recoil or stress induced inflammatory effects. For these effects one can place a stent in the vessel to prevent recoil as well as to provide a drug coating to prevent short term inflammatory reactions.